1. Field of the Invention
The present invention relates to encrypting data held by data storage devices.
2. Background Art
Protecting data from unauthorized access is becoming increasingly important. Both the amount and kinds of data generated and requiring protection continue to increase. Moreover, attacks by those not authorized to access the data grow in frequency and sophistication. An emerging need is for the encryption of data held in storage devices, referred to as “at-rest data encryption.”
Encryption works securely as long as the cipher text output is truly random. Anything that detracts from pure randomness helps an attacker. Most encryption algorithms feature two control inputs, the key which controls the encryption algorithm and an initialization vector that sets a “seed” for the encryption process. If the same key and the same initialization vector are used to encrypt data that has any repetitive structure, an attacker will see a repetitive structure in the encrypted data and will have a starting point for an attack.
One technique to avoid repetitive encrypted data is to use a nonce for the initialization vector that is different for every string encrypted. Nonce is a term used in encryption technology to refer to an initialization vector value that is unique for every data string that is encrypted. It need not be random, for example an incrementing value forms a valid nonce, but must be unique. Thus, even if every input string was identical, the encrypted data would be different for every string. The lack of repetition in the cipher text provides no opening for an attack.
Application of nonce-based encryption to a removable storage device, such as a tape drive, generates a particular problem for implementation since it is possible for a very large number of independent tape drives to be encrypting data using the same encryption key or keys. The requirement that the nonce be non-repeating in this environment creates a specific problem that must be addressed in the definition and implementation of the nonce.